The present invention relates to an electrophotographic copying device using a converging lens array as means to project the image of the original onto the recording medium.
Conventional electrophotographic copying machines form latent images by electrically charging a recording medium coated with a photo-conductive layer, then projecting a photographic image of the original onto the charged copying media. One device in the prior art uses an image-focussing lens which employs a specific focus distance f to transfer the photographic image reflected from the original through the lens and project it onto the recording medium. The expose the image of the original onto the copying media in an actual-size ratio, equal distances must be provided for the light path between lens and original and between lens and copying media, respectively. These light paths are usually provided with mirrors to ensure that the focus distance remains 2f, a technique requiring a considerably long light path. Thus the configuration of the entire unit must also be large, preventing smaller-sized copying machines.
To reduce unit size, some of the prior art devices use a converging lens array (henceforth called a lens array) as the means for projecting the image onto the recording medium. A lens array is placed between the original and the recording medium to focus the original image onto it. The length of the light path used by conventional lenses is thus reduced to allow incorporation in compact copiers. The lens array method can only be employed for actual-size ratio, however; enlargement and reduction of the original image on the copying medium is not possible using only one lens array. Installation of another lens array for variable-size copying makes it possible for a specific picture-forming device to produce copies in either actual- or variable-size. In this case, the user can choose the lens arrays according to the copy size ratio. When operating such a device, the leading edge of the copy paper and the image on the recording medium should be aligned with each other, requiring the copy paper to be fed at a different time according to the preferred scale ratio of the final copy. Because the image formation edge of the recording medium varies according to the magnification ratio, feeding of the copying paper must begin sooner when actual-size is desired than when size variation is desired. Means for controlling the copying-paper feeding operation therefore involves unavoidable complexity.